The present invention relates to an eddy-current measuring device, in particular a tachometer, which has a permanent magnet in the shape of a circular disk, the disk being positioned fixed for rotation on a drive shaft and, wherein at a slight distance from the disk, an eddy-current element of electrically conductive material is disposed fixed for rotation on a pointer shaft and, located behind the disk, there is a return element consisting of a magnetic material.
Such eddy-current measuring devices are generally known and used as tachometers in motor vehicles.
In the known devices of the above type the eddy-current element is developed as a bell which grips over a permanent magnet. The return element in the form of a stationary ring, and is arranged radially behind the bell. The permanent magnet is magnetized radially in order to produce eddy-currents in the eddy-current element.
The bell-shaped development of the eddy-current element provides the advantage that the gap width between eddy-current element and permanent magnet is constant at all times regardless of axial tolerances. However, the known measuring device has the disadvantage that it is of relatively large volume in radial direction since two structural parts grip with a spacing over the permanent magnet.